Refactor(hybrid gateway): Use generics in mapfuncs, index functions, and updating status

[randmonkey]

What this PR does / why we need it:
Use type generics instead of HTTPRoute only for supporting TLSRoute in the following places:

• index functions for controllers
• Map functions for controllers
• Setting status in hybrid gateway API converters
  Also updates the unit tests.

Which issue this PR fixes

Split from #3708

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect significant changes

[Copilot]

Pull request overview

Refactors hybrid gateway route handling to use generic helpers (instead of HTTPRoute-only implementations) in indexing, controller watch map functions, and status/ReferenceGrant handling—intended to enable future support for additional Gateway API route types (e.g., TLSRoute). Updates and reorganizes unit tests accordingly.

Changes:

• Introduces shared/generic route index utilities (e.g., GatewaysOnRoute) and updates HTTPRoute indexes to use them.
• Adds generic/shared map functions for Gateway/Service/EndpointSlice-to-route reconciliation wiring, and updates watchers to use them.
• Refactors route status helpers and ReferenceGrant checks to be route-kind aware; updates converter/target/status tests (including setting TypeMeta).

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
internal/utils/index/httproute.go	Switches HTTPRoute gateway index extraction to generic GatewaysOnRoute; backend service indexing uses shared backendRef helper.
internal/utils/index/httproute_test.go	Replaces old gateway-parentref tests with backendRef + plugin filter coverage; minor naming/typo issues.
internal/utils/index/gateway_route.go	Adds generic GatewaysOnRoute and shared backendRefToServiceKey.
internal/utils/index/gateway_route_test.go	Adds tests for generic GatewaysOnRoute and shared pointer helpers.
controller/hybridgateway/watch/watch.go	Updates HTTPRoute watchers to use generic MapRouteFor* map funcs.
controller/hybridgateway/watch/mapfuncs_httproute.go	Removes HTTPRoute-specific map funcs in favor of shared ones; updates KongPlugin mapfunc to call generic Kong resource mapper.
controller/hybridgateway/watch/mapfuncs_httproute_test.go	Updates index usage to GatewaysOnRoute.
controller/hybridgateway/watch/mapfuncs_gateway_route.go	Adds shared generic map funcs for Gateway/GatewayClass/Service/EndpointSlice and generic Kong resource mapper.
controller/hybridgateway/watch/mapfuncs_gateway_route_test.go	Adds tests for new shared map funcs (currently with indexing mismatch vs production).
controller/hybridgateway/target/target.go	Updates ReferenceGrant check call to pass backendRef + route kind.
controller/hybridgateway/target/target_test.go	Sets TypeMeta on test HTTPRoutes.
controller/hybridgateway/route/status.go	Generalizes multiple status/ReferenceGrant helpers; extracts BackendRef resolved condition logic; renames resolved-refs builder. (Contains a compile-breaking generic signature issue.)
controller/hybridgateway/route/status_test.go	Renames ReferenceGrant test and updates callsites; adds TypeMeta to many route fixtures; updates resolved-refs builder calls.
controller/hybridgateway/converter/http_route.go	Uses renamed resolved-refs builder function.
controller/hybridgateway/converter/http_route_converter_test.go	Sets TypeMeta on generated HTTPRoute fixtures.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Pull request overview

Copilot reviewed 15 out of 15 changed files in this pull request and generated 8 comments.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[tao12345666333]

Overall LGTM, left a comment